The vast majority of two-phase polymer blends form articles which are visually opaque and thus, cannot be used in applications requiring clarity. It is unusual to find blends of two polymers which form two-phase materials in the solid state and which are also visually clear.
Refractive indices of polymers vary over a broad range. For instance, many polymers have refractive indices in the range of 1.35 to 1.65. It is exceptional to find a pair of polymers where the refractive index difference is similar so that visually clear blends of the two immiscible components are formed.
It is known that the matching of refractive indices of polymer pairs can result in visually clear articles of the blends of the two polymers. L. Bohn, Polymer Handbook, 2nd ed., pp. 111-211, Wiley Interscience, New York ((1975); J. MacKnight et al., Polymer Blends, Vol. I, p. 185, Academic Press, New York (1978). Biangardi et al., Die Angew. Makromole. Chemie, 183, 221 (1990), have developed model calculations which quantify this phenomena and evaluate the light scattering of certain blends as a function of particle diameter, refractive index, wavelength, and particle structure.
Bauer et al., Adv. Chem. Ser., 99, 251 (1971), report transparent blends which were prepared from poly(methyl methacrylate) and diene elastomers. Skochdopole et al., et al., Polym. Engr. Sci., 27, 627 (1987), reported a blend of polycarbonate and styrene-acrylonitrile which was transparent due to a near match of the refractive indices of the two materials. Tse et al., J. Appl. Polym. Sci., 42, 1205 (1991), disclosed blends of poly(vinyl chloride) and chlorinated polyethylene which were translucent due to a close match of refractive indicies.
Clear composites have been reported also. See Breuer and Grzesitza, Die Angew. Makromol. Chemie, 45, 1 (1975). U.S. Pat. No. 4,581,288 (1986) disclosed lens materials which were composites of glass and plastic with refractive indices matched to .+-.0.0020. U.S. Pat. No. 3,441,525 [1969] disclosed glass composites based on diallylic phthalate polymers where the refractive indices were sufficiently matched to yield clear materials. Linet al., Polym. Engr. Sci., 37, 344 (1992) reported the preparation of transparent poly(methyl methacrylate) composites by matching the refractive index of the glass fiber reinforcement to the refractive index of the poly(methyl methacrylate) matrix.
There is a need in the art for visually clear, two-phase blends which are particularly useful in applications requiring tough weather resistant material.